Edit in JSFiddle

var cont = document.getElementById('rs')
var ln = `\n`
var line = `\n${'#'.repeat(64)}\n`
var maxArgs = function(first, second){
	cont.textContent += line
  cont.textContent += ln + `first === arguments[0]: ` + (first === arguments[0])
  cont.textContent += ln + `second === arguments[1]: ` + (second === arguments[1])
  
  first = "c";
  second = "d";
  cont.textContent += ln + `first === arguments[0]: ` + (first === arguments[0])
  cont.textContent += ln + `second === arguments[1]: ` + (second === arguments[1])
}
var mixArgs = function(first, second){
	"use strict"
	cont.textContent += line
  cont.textContent += ln + `first === arguments[0]: ` + (first === arguments[0])
  cont.textContent += ln + `second === arguments[1]: ` + (second === arguments[1])
  
  first = "c";
  second = "d";
  cont.textContent += ln + `first === arguments[0]: ` + (first === arguments[0])
  cont.textContent += ln + `second === arguments[1]: ` + (second === arguments[1])
}
var makeReq = function(url, timeout, callback){
	timeout = timeout || 2000;
  callback = callback || function(){};
  
  cont.textContent += line
  cont.textContent += `#makeReq()`
  cont.textContent += ln + `url: ${url}`
  cont.textContent += ln + `timeout: ${timeout}`
  cont.textContent += ln + `callback: ${callback}`
}
var makeRequest = function(url, timeout = 2000, callback = function(){}){
  
  cont.textContent += line
  cont.textContent += `#makeRequest()`
  cont.textContent += ln + `url: ${url}`
  cont.textContent += ln + `timeout: ${timeout}`
  cont.textContent += ln + `callback: ${callback}`
}
var getTimeout = function(val = 0){
  cont.textContent += line
  cont.textContent += `#getTimeout()`
	return val + 5
}

var echoPrimitive = function(url, timeout = getTimeout()){
  cont.textContent += line
  cont.textContent += `#echoPrimitive()`
  cont.textContent += ln + `url: ${url}`
  cont.textContent += ln + `timeout: ${timeout}`
}

maxArgs( "a", "b")
mixArgs( "a", "b")
makeReq("/foo")
makeReq("/foo", 500)
makeReq("/foo", 500, function(body){
	cont.textContent += `makeReq("${body}")`
})
makeRequest("/foo")
makeRequest("/foo", 500)
makeRequest("/foo", 500, function(body){
	cont.textContent += `makeRequest("${body}")`
})
echoPrimitive("/foo")



var add = function(first, second = first){
	cont.textContent += line
	cont.textContent += `#add()`
  cont.textContent += ln + `first: ${first}`
  cont.textContent += ln + `second: ${second}`
}
var addTDZ = function(first = second, second){	// temporal dead zone
	cont.textContent += line
  cont.textContent += `#addTDZ()`
  cont.textContent += ln + `first: ${first}`
  cont.textContent += ln + `second: ${second}`
}

add(3)
add(3, 5)
addTDZ(3)
addTDZ(3, 5) // Error

<pre id="rs"></pre>